I no this is a really old site but I'm going to try to get a gold fish at the fair tomorrow. If I win I'm going to put it in a 20 gallon tank. My tank doesn't have a filter, is it necessary to have a filter? Can I add a filter to it or will I need to buy another one if it's necessary? Also, anyone no how much feed cost and does it need bed rocks, plants,another fish as a friend,etc? Thanks for any help.
What can do and what you should do are two entirely different things... Yes you could put the goldfish in the tank without a filter (as many do) but it's far from a good environment for the fish, in fact IMO it's animal cruelty and should never be done, the water quality will deteriorate very fast, causing stunted growth, shorter lifespan, irritation, ailments and illnesses and even death...
A feeder gold fish in a good water and fed properly will grow to about a 4" body length (not including tail fin) in about a year, in two years time in a good environment and clean water it will grow to about 9" in length (not including the tail fine)... With that said your 20 gallon tank will only suffice for about two years max if you take good care of the goldfish before it becomes realistically too small and will need a bigger tank... But a vast majority of people never provide ideal aquarium environments and the fishes growth is stunted due to this, and that isn't ideal either...
That said with a single small gold fish fed properly and not too much you could maintain passable water quality without a filter if you did daily or every other day 50% water changes, but even then there will be ammonia, nitrate, nitrite and PH spikes that are not healthy in any regard for the fish...
You can get a hang on back filter at
Walmart for CHEAP, and although it's not the best filter option it's light years better than no filtration... Even with a filter you should do 25% water changes every week or two...
As for tank decoration, to be blunt bare tanks are best for goldfish (as well as most fish) as they are easier to keep clean and provide less places for nasties to build up... Goldfish will likely eat any live plants you put in, so they won't last long... As for a tank mate, IMO no more than 2 goldfish in your 20 gallon tank in the first two years, they will quickly outgrow that tank after the 2nd year and produce excess levels of waste for that volume of water unless you have a superb filtration system...
As for cost, only a few dollars a year in fish food for the first year or two and it grows from there, but not all that much, even at a foot long the feed cost is minimal over a year...
Now, I know there is someone that has done this or that with no filter and no water changes and the fish lived to that I say living does not mean it was properly taken care of or given a decent quality of life...
And last but not least don't get your hopes up that it will survive, the stress, water conditions and a slew of other handling factors are against a 'carnival/fair' give away fish's survival... Especially when you don't have a properly cycled tank to put them into when you get home, it can take a month for a tank to cycle property and build up enough good bacteria in the filter to control the waste, until that happens you really need to focus on frequent and large percentage water changes... Google up how to cycle a fish tank and please don't believe that there is a fix in a bottle, the only proper way to cycle a fish tank is to establish a healthy beneficial bacteria colony in the filter, that takes time...
If you do get a hang on back filter as I highly suggest you do, don't follow the instructions on changing the filter (they are geared towards return profits for the filter company, not the fishes health) when you notice the filter is getting 'clogged' or dirty, simply take the filter media out an run it under luke warm water in the sink and lightly brush off the build up then put it back in the tank... Don't run it under hot or cold water or scrub it entirely clean, you only want to get rid of the easy to remove build up not the established living beneficial bacteria colony on the filter... Doing this the filter media in a hang on back filter will easily last a year or even longer... And when it does come time to change the filter cut a section of the old filter (the bigger the better) off an put it behind the new filter and touching the new filter, this will allow the bacteria to transfer to the new filter and establish a colony on the new filter faster....
